The present invention relates to a drum heater with rotary drum and hot gas burner for blowing hot gases into the rotary drum interior fitted with at least one hot gas conduit segment, in particular for asphalt recycling.
Asphalt road surfaces are manufactured with minerals being heated in a drying drum and then mixed in another mixing drum with hot bitumen and with the mixture then heated to a temperature of approximately 150xc2x0 C. With the temperature of 120xc2x0 C. to 180xc2x0 C. required for making asphalt road surfaces the asphalt is a viscous liquid product, whereby the bitumen constituents encase the minerals and bond into a solid mass after cooling to form a viscous, wear-resistant road surface.
Asphalt is understood in this invention to mean road asphalt having a lesser bitumen proportion of approximately less than 5% by weight.
If, however, the asphalt is subjected to high temperatures during the heating procedure, such as e.g. a direct flame, the asphalt then carbonises. This coking of the asphalt is undesired, as this releases smoke and contaminated waste gases and the binding capacity of the asphalt is reduced. For the purposes of rapid heating of large quantities of road surface asphalt compositions high temperatures must be applied to cause rapid heating of the asphalt mixture.
The drum heater according to the present invention is also suited to the additional task of drying and heating of other granular materials. Applying indirect hot gas heating on the one hand guarantees rapid and economical readiness and on the other hand enables environmentally friendly treatment; without material combustion gases or cracked gases being released. Indirect heating makes it possible to avoid excess temperatures and material combustion in the material to be recycled/treated.
The asphalt to be prepared and fed to the rotary drum comprises a bituminous mixture comminuted into different lump sizes by mechanical crushing or pulverizing plants. The material to be prepared is generally 40xc3x9740 centimeters in size, e.g. with an asphalt cover thickness of up to 10 centimeters.
Drum heaters with blowpipe burner, oil or gas flame heating are known for heating asphalt recycling granulate. Diverse configurations of such drum heaters are known from the prior art, which have cylindrical rotary drums. Arranged fixed on a front face of the cylindrical rotary drum, approximately at the level of the axis of rotation, is a burner with a hot gas flame directed into the interior of the rotary drum. The other rotary drum end is fitted with a delivery opening, via which the hot gas flows out and at the same time preheats or dries the asphalt lumps to be supplied for comminution. The comminuted or molten asphalt leaves the rotary drum in the vicinity of the rotary drum end on which the hot gas burner is arranged.
With conventional rotary drum heaters the burner heat is often not fully utilised, because the insufflated hot gases exit from the rotary drum interior too quickly. The exit of the hot gases is often hindered only slightly by the introduced asphalt lumps to be processed and these lumps can be impacted directly by the burner flame.
In the prior art various solutions have already been proposed for better utilisation of burner heat. U.S. Pat. No. 5,083,870-A, for its German equivalent DE 42 00 760-C2, for example, describe a road asphalting machine for making an asphalt surface, having a rotatable cylindrical mixing drum, divided into two chambers by a partition extending through the rotary drum. The material fed to the rotary drum for heating is prewarmed in the fore section of the heating chamber and latent heat is recovered from the water vapour in the heating chamber exhaust. The second chamber has a plurality of burners arranged beneath the rotary drum and aligning with the rotary drum axis. Each heater is partially separated by zone separation plates from the adjoining heaters. The heaters are swivel-mounted on a frame, on which the heating chamber and the rotary drum are arranged and can be rotated to change the angle at which the burner flame affects the rotary drum. Quadrant plates subdivide the rotary drum along its axis to form four identical rotary drum quadrants. The quadrant plates have through-slots for material to pass through from one quadrant to another. The material in the rotary drum is heated in countercurrent by the combustion gases from the burners in the heating section of the chamber.
It is the object of the present invention to provide a rotary drum of the type initially outlined, which better utilizes the heat of the introduced hot gases and avoids direct contact of the asphalt lumps with the burner flame and at the same time enables the simplest possible rotary drum interior. The aim is to enable gentle heating and intermixing of the asphalt break-up and/or if required other granular materials to be prepared, in which the bituminous mixture is subjected to a minimal grinding effect only with the most even and extensive indirect heating possible.
It was surprisingly ascertained that this task is solved according to the present invention in that arranged inside the rotary drum interior is a unipart or multipart hot gas conduit segment which has at least one hot gas surface of impingement which extends from the rotary drum inner wall to the rotary drum interior and is aligned in the direction of the hot gas flow. The hot gas is insufflaled preferably substantially parallel to the longitudinal axis of rotation of the rotary drum. The invention is characterised by claim 1. Preferred Embodiments are the subject of the sub-claims.